Polishing apparatus and method for polishing semiconductor wafers using load-unload stations

ABSTRACT

A polishing apparatus and method for polishing semiconductor wafers uses multiple load-unload stations and at least one turn-over robotic wafer handing device to process the wafers so that the wafer can be polished at multiple polishing tables. The turn-over robotic wafer handing device operates to turn over the wafers so that one side of the wafers can be polished at a first polishing table and the other side of the wafers can then be polished at a second polishing table.

CROSS REFERENCE TO RELATED APPLICATION

This application is entitled to the benefit of U.S. Provisional Patent Application Ser. No. 60/967,472, filed on Sep. 5, 2007, which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates generally to semiconductor processing equipments, and more particularly to a polishing apparatus and method for polishing semiconductor wafers.

BACKGROUND OF THE INVENTION

Wet cleaning methods that use liquid chemicals have been used to remove particles from both sides of semiconductor wafers. However, particles embedded in the semiconductor wafers are not easily removed by conventional wet cleaning methods.

Chemical Mechanical Polishing (CMP) technology, which is used to planarize surfaces of semiconductor wafers, can be used to remove such particles. In general, a conventional CMP apparatus includes a polishing table where a polishing pad is placed, and a wafer carrier that supports a semiconductor wafer, which is polished by pressing the wafer against the polishing pad. The CMP apparatus also includes a wafer cleaner to clean and dry the polished wafers.

However, the conventional CMP apparatus is designed to polish only the front sides of the semiconductor wafers, which are the sides where semiconductor devices are formed on the wafers, in order to planarize surface layers deposited on the front sides of the wafers. Thus, if the conventional CMP apparatus is to be used to remove particles from both sides of the semiconductor wafers, the wafers must be processed twice in the CMP apparatus to polish both sides of the wafers.

In order to polish the front sides of the wafers, the wafers are loaded into the CMP apparatus and then polished such that the front sides of the wafers are polished. The polished wafers are then cleaned and dried in the wafer cleaner before the wafers are removed from the CMP apparatus. In order to polish the backsides of the wafers, the wafers removed from the CMP apparatus must be loaded into the CMP apparatus again and then polished such that the backsides of the wafers are polished. The polished wafers must then be cleaned and dried again in the wafer cleaner before the wafers are removed from the CMP apparatus.

In view of this issue, what is needed is a polishing apparatus and method for polishing semiconductor wafers that can polish both sides of the wafers in a more efficient manner.

SUMMARY OF THE INVENTION

A polishing apparatus and method for polishing semiconductor wafers uses multiple load-unload stations and at least one turn-over robotic wafer handing device to process the wafers so that the wafer can be polished at multiple polishing tables. The turn-over robotic wafer handing device operates to turn over the wafers so that one side of the wafers can be polished at a first polishing table and the other side of the wafers can then be polished at a second polishing table.

A polishing apparatus in accordance with an embodiment of the invention comprises first and second polishing units, first, second, third and fourth load-unload stations and a turn-over robotic wafer handing device. Each of the first and second polishing units is configured to polish one side of semiconductor wafers. Each of the first and second polishing units comprises a polishing table and a wafer carrier assembly configured to hold a semiconductor wafer and move the semiconductor wafer to and from the polishing table. The wafer carrier assembly is further configured to move the semiconductor wafer onto the polishing table. Each of the first, second, third and fourth load-unload stations is configured to accommodate one of the semiconductor wafers at a time. The first and second load-unload stations are situated such that the first polishing unit is positioned between the first and second load-unload stations. The third and fourth load-unload stations are situated such that the second polishing unit is positioned between the third and fourth load-unload stations. The turn-over robotic wafer handing device is positioned between the second and third load-unload stations. The turn-over robotic wafer handing device is configured to transfer the semiconductor wafer from the second load-unload station to the third load-unload station. The turn-over robotic wafer handing device is further configured to turn over the semiconductor wafer when the semiconductor wafer is transferred from the second load-unload station to the third load-unload station.

A method for polishing semiconductor wafers in accordance with an embodiment of the invention comprises moving a semiconductor wafer between a first load-unload station, a first polishing table and a second load-unload station on a first wafer carrier assembly, including polishing a first side of the semiconductor wafer on the first polishing table using the first wafer carrier assembly, moving the semiconductor wafer between a third load-unload station, a second polishing table and a fourth load-unload station on a second wafer carrier assembly, including polishing a second side of the semiconductor wafer on the second polishing table using the second wafer carrier assembly, and transferring the semiconductor wafer from the second load-unload station to the third load-unload station using a turn-over robotic wafer handing device, including turning over the semiconductor wafer when the semiconductor wafer is transferred from the second load-unload station to the third load-unload station.

Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a polishing apparatus in accordance with an embodiment of the present invention.

FIG. 2 is a side view of polishing units and load-unload stations of a polishing station of the polishing apparatus of FIG. 1, illustrating how wafer carrier assemblies of the polishing units linearly move to transfer semiconductor wafers.

FIG. 3 is a top view of a load-unload station in accordance with an embodiment of the invention, which can be used in the polishing apparatus of FIG. 1.

FIG. 4 is a cross-sectional view of the load-unload station of FIG. 3.

FIGS. 5( a) and 5(b) are sequential cross-sectional views of the load-unload station of FIG. 3 to show a sequence of loading a semiconductor wafer W onto a wafer carrier.

FIG. 6 is a top view of a polishing station in accordance with an alternative embodiment of the present invention.

FIGS. 7 and 8 are top view of a wafer turn-over device in accordance with an embodiment of the invention, which shows a semiconductor wafer being transferred between two load-unload stations of the polishing apparatus of FIG. 1 such that the semiconductor wafer is also turned over.

FIG. 9 is a cross-sectional view of the wafer turn-over device of FIGS. 7 and 8.

FIG. 10 is a top view of the wafer turn-over device in accordance with another embodiment of the invention.

FIG. 11 is a top view of a polishing station in accordance with another alternative embodiment of the present invention.

FIG. 12 is a top view of a washing station of the polishing station of FIG. 11 in accordance with an embodiment of the invention.

FIG. 13 is a flow diagram of a method of polishing semiconductor wafers in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, a polishing apparatus 10 in accordance with an embodiment of the present invention is described. FIG. 1 is a top view of the polishing apparatus 10. FIG. 2 is a side view of a polishing station 20 of the polishing apparatus 10. The polishing apparatus 10 comprises the polishing station 20, a wafer storage station 102, an input buffer station 105, a first wafer transport device 150, a second wafer transport device 160, a third wafer transport device 210, a first wafer cleaner 220, and a second wafer cleaner 220′.

The polishing station 20 is an enclosed structure with window-like mechanisms (not shown) that can be opened to transfer semiconductor wafers into and out of the polishing station 20. The polishing station 20 comprises a first polishing unit 250 a, a second polishing unit 250 b, first two load-unload stations 15 a and 15 a′, second two load-unload stations 15 b and 15 b′, third two load-unload stations 15 c and 15 c′, fourth two load-unload stations 15 d and 15 d′, and a wafer turn-over device 50. In the following description, similar components will sometimes be referred to herein using their common reference numbers without the letter suffixes.

Each polishing unit 250 of the polishing station 20 comprises a polishing table 256, a first wafer carrier assembly 260 and a second wafer carrier assembly 260′. The polishing table 256 can be used to simultaneously polish two semiconductor wafers at a time. The polishing table 256 can be rotated or orbited about an axis. In some embodiments, a polishing pad 255 may be attached to the polishing table 256 for chemical and mechanical polishing process of semiconductor wafers. One or more slurries containing abrasive particles and/or chemicals, such as potassium hydroxide (KOH), may be used with the polishing pad 255 to polish semiconductor wafers. Each polishing unit 250 may further comprise a pad conditioner (not shown) to condition the surface of the polishing pad 255 during the polishing process to refresh the surface of the polishing pad for proper polishing.

Each wafer carrier assembly 260 of the polishing units 250 a and 250 b comprises a wafer carrier 262, a carrier shaft 264 and a rotational-and-vertical drive mechanism 266, as illustrated in FIGS. 1 and 2. The wafer carrier 262 is designed to hold a semiconductor wafer such that the surface of the wafer to be polished is faced toward the polishing pad 255. The wafer carrier 262 is connected to the rotational-and-vertical drive mechanism 266 through the carrier shaft 264. The rotational-and-vertical drive mechanism 266 controls the rotational and vertical motions of the wafer carrier 262 through the connected carrier shaft 264. Thus, the rotational-and vertical drive mechanism 266 is configured to rotate the wafer carrier 262 by rotating the connected carrier shaft 264 and to vertically move the wafer carrier 262 by vertically moving the connected carrier shaft 264. In order to polish semiconductor wafers, the wafer carriers 262 are moved down or lowered to the respective polishing pads 255 by the respective rotating-and-vertical mechanisms 266 to press the wafers held by the wafer carriers 262 onto the respective polishing pads 255.

The load-unload stations 15 of the polishing station 20 accommodate wafers transferred to and from the load-unload stations 15. Each of the load-unload stations 15 is configured to accommodate one semiconductor wafer at at time. The load-unload stations 15 are configured to receive or unload a wafer released from a wafer carrier 262 or another device, such as the second wafer transport device 160, and to place or load a wafer onto a wafer carrier or another device.

The load-unload stations 15 and the two polishing units 250 a and 250 b are arranged in such a manner that the first two load-unload stations 15 a and 15 a′ are positioned in front of the first polishing unit 250 a (i.e., closest to the second wafer transport device 160), the second two load-unload stations 15 b and 15 b′ are positioned between the first polishing unit 250 a and the third two load-unload stations 15 c and 15 c′, the second polishing unit 250 b is positioned between the third two load-unload stations 15 c and 15 c′ and the fourth two load-unload stations 15 d and 15 d′, and the fourth load-unload stations 15 d and 15 d′ are positioned behind the second polishing unit 250 b, as illustrated in FIG. 1. In addition, the load-unload stations 15 a, 15 b, 15 c and 15 d are arranged in a linear manner, and the load-unload stations 15 a′, 15 b′, 15 c′ and 15 d′ are also arranged in a linear manner. That is, the load-unload stations 15 a, 15 b, 15 c and 15 d are aligned along a straight line, and the load-unload stations 15 a′, 15 b′, 15 c′ and 15 d′ are aligned along another straight line.

The polishing station 20 is configured such that (1) the first wafer carrier assembly 260 a of the first polishing unit 250 a can move in a linear manner between the first and second load-unload stations 15 a and 15 b, and the first wafer carrier assembly 260 b of the second polishing unit 250 b can move in a linear manner between the third and fourth load-unload stations 15 c and 15 d, and (2) the second wafer carrier assembly 260 a′ of the first polishing unit 250 a can move in a linear manner between the first and second load-unload stations 15 a′ and 15 b′ and the second wafer carrier assembly 260 b′ of the second polishing unit 250 b can move in a linear manner between the third and fourth load-unload stations 15 c′ and 15 d′.

The polishing station 20 can be also configured such that (1) the first wafer carrier assembly 260 a of the first polishing unit 250 a can also move in a linear manner between the first, second and third load-unload stations 15 a, 15 b and 15 c, and the first wafer carrier assembly 260 b of the second polishing unit 250 b can move in a linear manner between the second, third and fourth load-unload stations 15 b, 15 c and 15 d, and (2) the second wafer carrier assembly 260 a′ of the first polishing unit 250 a can move in a linear manner between the first, second and third load-unload stations 15 a′, 15 b′ and 15 c′ and the second wafer carrier assembly 260 b′ of the second polishing unit 250 b can also move in a linear manner between the second, third and fourth load-unload stations 15 b′, 15 c′ and 15 d′.

In order to move the wafer carrier assemblies 260 linearly between the load-unload stations 15, the wafer carrier assemblies 260 are connected to at least one wafer conveying device 22, as shown in FIG. 2, which can move the wafer carrier assemblies linearly. An example of a wafer conveying device that can be used to linearly move the wafer carrier assemblies 260 is described in U.S. Pat. No. 7,223,153, which is incorporated herein by reference.

With reference to FIGS. 3-5, one of the load-unload stations 15 of the polishing station 20 is further described. FIG. 3 is a top view of the load-unload station 15, and FIG. 4 is a cross-sectional view of the load-unload station 15 of FIG. 3 along the line QQ. The load-unload station 15 comprises a base 190, an annular wall 195, a lifter 200, a wafer tray 211, first multiple nozzles 240, second multiple nozzles 250, a drain channel 260, a first fluid channel 270 and a second fluid channel 272. The fluid channels 270 and 272 may be connected to fluid sources (not shown). The drain channel 260 may be connected to a drain pump (not shown).

The annular wall 195 and the wafer tray 211 are mounted on the base 190. The wafer tray 211 comprises a hole at the center such that the lifter 200 can be positioned at the center of the base 190. The lifter 200 is connected to a lifter pneumatic cylinder 204 through a lift piston 202, as illustrated in FIG. 4. The lifter 200 is a wafer handling device to raise and lower a wafer to and from a wafer carrier (also known as a polishing head), such as one of the wafer carriers 262 a, 262 a′, 262 b and 262 b′. The lifter cylinder 204 is connected to the first fluid channel 270 and operated by a fluid supplied through the first fluid channel 270. The lifter 200 is moved up and down by the lifter cylinder 204.

The lifter 200 is lifted above the top surface of the annular wall 195 to a wafer transfer position, as illustrated in FIG. 4, to receive a semiconductor wafer W from a wafer transport device, such as the second wafer transport device 160, from a wafer carrier, such as one of the wafer carriers 262 a, 262 a′, 262 b and 262 b′, or from a wafer turn-over device, such as the wafer turn-over device 50. After the lifter 200 receives the wafer W, the lifter is moved down below the wafer tray 211 in order to place the wafer W on the wafer tray 211. In this fashion, the wafer W is unloaded onto the load-unload station 15.

To transfer the wafer W from the lifter 200 to a wafer transport device, such as the third wafer transport device 210, to a wafer carrier, such as one of the wafer carriers 262 a, 262 a′, 262 b and 262 b′, or to a wafer turn-over device, such as the wafer turn-over device 50, the lifter 200 is lifted above the top surface of the annular wall 195 to the wafer transfer position, as illustrated in FIG. 4.

The first multiple nozzles 240 are mounted on the top of the base 190 and the second multiple nozzles 250 are mounted on the interior side of the annular wall 195, as illustrated in FIG. 4. The first and second nozzles 240 and 250 are connected to the second fluid channel 272 and used to spray fluid, such as deionized (D.I.) water, which is supplied through the second fluid channel 272. Used fluid, e.g., used D.I. water, is drained through the drain channel 260 by the drain pump (not shown). The first and second multiple nozzles 240 and 250 allow the load-unload station 15 to wash a wafer and/or a wafer carrier, when one or both are positioned at the load-unload station 15.

With reference to FIGS. 5( a) and 5(b), a process sequence for loading a semiconductor wafer W from the load-unload station 15 of FIGS. 3 and 4 onto a wafer carrier 262, which can be one of the wafer carriers 262 a-262 b′ is described. FIGS. 5( a) and (b) are sequential cross-sectional views of the load-unload station 15. After the wafer W is positioned on the wafer tray 211 of the load-unload station 15, as previously described with reference to FIG. 4, the wafer carrier 262 is placed on the load-unload station 15, as illustrated in FIG. 5( a). As shown in FIG. 5( a), the wafer carrier 262 may include a retainer ring 280 to confine the wafer W during a polishing process. Next, the lifter 200 is moved up and the wafer W on the lifter is received by the wafer carrier 262 using a vacuum supplied through vacuum channels 285, as illustrated in FIG. 5( b). After the wafer W is received by the wafer carrier 262, the lifter 200 is moved down. For unloading the wafer W from the wafer carrier 262, the vacuum provided through the vacuum channels 285 is removed, which releases the wafer W from the wafer carrier 262 onto the lifter 200 of the load-unload station 15. The load-unload station 15 can then wash the wafer carrier 262 by spraying D.I. water onto the wafer carrier 262.

Turning back to FIGS. 1 and 2, the wafer turn-over device 50 is situated between the second two load-unload stations 15 b and 15 b′ and the third two load-unload stations 15 c and 15 c′. The wafer turn-over device 50 is a robotic wafer handling device that is configured to transfer wafers from the second two load-unload stations 15 b and 15 b′ to the third two load-unload stations 15 c and 15 c′. A robotic arm 51 of the turn-over device 50 can reach the second two load-unload stations 15 b and 15 b′ to pick up the wafers from the second two load-unload stations 15 b and 15 b′. The robotic arm 51 of the wafer turn-over device 50 is further configured to turn over the wafers after it picks up the wafers from the second two load-unload stations 15 b and 15 b′ such that it can transfer the wafers to the third two load-unload stations 15 c and 15 c′ after it turns over the wafers. As used herein, turning over a semiconductor wafer means that the wafer is rotated 180 degrees so that major sides or surfaces of the wafer are reversed. For example, if the front side of the wafer is initially facing downward, the front side of the wafer will be facing upward after the wafer is turned over.

The wafer cleaners 220 and 220′ are enclosed structures with window-like mechanisms (not shown) that can be opened to transfer semiconductor wafers into and out of the wafer cleaners. The first wafer cleaner 220 comprises a wafer receiving station 222, a first cleaning station 224, a second cleaning station 226, a drying station 228, an output buffer station 230, a first wafer transport device 232, a second wafer transport device 234, a third wafer transport device 236, and a fourth wafer transport device 238. The wafer cleaner 220 is configured to clean and dry both of the front and back sides of the wafers. The second wafer cleaner 220′ can be identical to the first wafer cleaner 220.

The wafer cleaners 220 and 220′ are situated such that the wafer receiving stations 222 of the wafer cleaners are adjacent to the third wafer transport device 210 and the output buffer stations 230 of the wafer cleaners are adjacent to the first wafer transport device 150.

The wafer receiving station 222 accommodates semiconductor wafers that are transferred by the third wafer transport device 210. The first wafer transport device 232 transfers wafers from the wafer receiving station 222 to the first cleaning station 224. The second wafer transport device 234 transfers wafers from the first cleaning station 224 to the second cleaning station 226. The third wafer transport device 236 transfers wafers from the second cleaning station 226 to the drying station 228. The fourth wafer transport device 238 transfers wafers from the drying station 228 to the output buffer station 230. Wafers are removed from the output buffer station 230 by the first wafer transport device 150 and then transferred to the wafer storage station 102.

The first and second cleaning stations 224 and 226 of the wafer cleaner 220 remove slurry particles from wafer surfaces using D.I. water and/or chemicals, such as ammonium hydroxide (NH₄OH), diluted hydrofluoric acid (HF) and organic chemicals. The wafer receiving station 222 can be also configured to remove slurry particles from wafer surfaces using D.I. water and/or chemicals, such as NH₄OH, diluted HF and organic chemicals. After the cleaning process is completed at the second cleaning station 226, wafers are rinsed with D.I. water and then dried in the drying station 228.

The wafer storage station 102 accommodates semiconductor wafers or other comparable objects to be polished by the polishing station 20. The wafer storage station 102 can also accommodate semiconductor wafers or other comparable objects that have been polished and cleaned by the polishing station 20 and the wafer cleaners 220 and 220′.

The first wafer transport device 150 is situated between the wafer storage station 102 and the input buffer station 105 and between the wafer storage station 102 and the wafer cleaners 220 and 220′, as illustrated in FIG. 1, such that a robotic arm of the first wafer transport device 150 can transfer wafers from the wafer storage station 102 to the input buffer station 105 and from output buffer stations 230 of the wafer cleaners 220 and 220′ to the wafer storage station 102.

The input buffer station 105 is situated between the first and second wafer transport devices 150 and 160. The input buffer station 105 accommodates wafers to be polished by the polishing station 20.

The second wafer transport device 160 is situated between the input buffer station 105 and the first two load-unload stations 15 a and 15 a′ of the polishing station 20, as illustrated in FIG. 1, such that a robotic arm of the second wafer transport device 160 can transfer wafers from the input buffer station 105 to the first load-unload stations 15 a and 15 a′ of the polishing station 20. Because the robotic arm of the second wafer transport device 160 can be contaminated when it enters the polishing station 20, the second wafer transport device 160 is preferably separated from the first wafer transport device 150 by a partition 161, as illustrated in FIG. 1, in order to prevent the second wafer transport device 160 from contaminating the first wafer transport device 150. In order to keep the first wafer transport device 150 clean, an air filter unit (not shown) can be installed over the first wafer transport device 150.

The third wafer transport device 210 is situated between the fourth load-unload stations 15 d and 15 d′ of the polishing station 20 and the wafer receiving stations 222 of the respective wafer cleaners 220 and 220′, as illustrated in FIG. 1, such that a robotic arm of the third wafer transport device 210 can transfer wafers from the fourth two load-unload stations 15 d and 15 d′ to the wafer receiving stations 222.

The first and third wafer transport devices 150 and 210 may be situated on respective linear tracks 155 and 215 such that the wafer transport devices can be moved in a linear manner on the linear tracks by respective linear drive mechanisms (not shown). The robotic arms of the first, second and third wafer transport devices 150, 160 and 210 may be configured to turn over wafers before transferring the wafers to the input buffer station 105, the polishing station 20 and the wafer cleaners 220 and 220′, respectively.

With reference to FIGS. 1 and 2, a method of processing semiconductor wafers in the polishing apparatus 10 according to an embodiment of the present invention is described.

First, the first wafer transport device 150 transfers semiconductor wafers from the storage station 102 to the input buffer station 105.

Next, the second wafer transport device 160 transfers the wafers from the input buffer station 105 to the first two load-unload stations 15 a and 15 a′ such that backsides of the wafers, where transistors and electrical circuits are not formed, face the first load-unload stations 15 a and 15 a′. That is, the backsides of the wafers are faced downward toward the first load-unload stations 15 a and 15 a′.

Next, the wafer carriers 262 a and 262 a′ of the first polishing unit 250 a (1) move linearly to the first two load-unload stations 15 a and 15 a′, respectively, (2) receive the wafers from the first load-unload stations 15 a and 15 a′, and then (3) move to the polishing table 256 a of the first polishing unit 250 a.

Next, the wafer carriers 262 a and 262 a′ move down to the polishing pad 255 a of the polishing table 256 a and then polish the wafers using a first slurry. Thus, the backsides of the wafers are polished on the polishing pad 255 a.

Next, after the wafers are polished on the polishing pad 255 a, the wafer carriers 262 a and 262 a′ move up from the polishing pad 255 a.

Next, the wafer carriers 262 a and 262 a′ of the first polishing unit 250 a (1) move linearly to the second two load-unload stations 15 b and 15 b′, respectively, (2) transfer the wafers to the second load-unload stations 15 b and 15 b′ such that the backsides of the wafers face the second load-unload stations 15 b and 15 b′, and then (3) return to the first load-unload stations 15 a and 15 a′.

Next, the robotic arm of the wafer turn-over device 50 (1) approaches the second load-unload station 15 b, (2) picks up the wafer from the second load-unload station 15 b, (3) turns over the wafer such that the backside of the wafer faces upward, (4) transfers the wafer to the third load-unload station 15 c such that the front side of the wafer, where transistors and electrical circuits are formed, faces the third load-unload station 15 c, (5) approaches the second load-unload station 15 b′, (6) picks up the wafer from the second load-unload station 15 b′, (7) turns over the wafer such that the backside of the wafer faces upward, (8) transfers the wafer to the third load-unload station 15 c′ such that the front side of the wafer, where transistors and electrical circuits are formed, faces the third load-unload station 15 c′, and (9) moves away from the third load-unload station 15 c′.

Next, the wafer carriers 262 b and 262 b′ of the second polishing unit 250 b (1) move linearly to the third load-unload stations 15 c and 15 c′, respectively, (2) receive the wafers from the third load-unload stations 15 c and 15 c′, and then (3) move to the polishing table 256 b of the second polishing unit 250 b.

Next, the wafer carriers 262 b and 262 b′ move down to the polishing pad 255 b of the polishing table 256 b and then polish the wafers using a second slurry, whose components are different from the first slurry. Alternatively, the first slurry used at the polishing table 256 a can be used at the polishing table 256 b instead of the second slurry. Thus, the front sides of the wafers are polished on the polishing pad 255 b.

Next, after the wafers are polished on the polishing pad 255 b, the wafer carriers 262 b and 262 b′ move up from the polishing pad 255 b.

Next, the wafer carriers 262 b and 262 b′ of the second polishing unit 250 b (1) move linearly to the fourth load-unload stations 15 d and 15 d′, respectively, (2) transfer the wafers to the fourth load-unload stations 15 d and 15 d′ such that the front sides of the wafers face the fourth load-unload stations 15 d and 15 d′, and then (3) return to the third load-unload stations 15 c and 15 c′.

Next, the third wafer transport device 210 removes the wafers from the fourth load-unload stations 15 d and 15 d′ and then transfers the wafers to the wafer receiving stations 222 of the wafer cleaners 220 and 220′, respectively. The third wafer transport device 210 may turn over the wafers before transferring the wafers to the wafer receiving stations 222. The wafers are then cleaned and dried in the wafer cleaners 220 and 220′.

Next, the first wafer transport device 150 removes the wafers from the output buffer stations 230 of the wafer cleaners 220 and 220′ after the wafer have been processed in the wafer cleaners 220 and 220′.

Next, the first wafer transport device 150 transfers the wafers to the storage station 102.

In this embodiment, the backsides of the wafers have been first polished in the first polishing unit 250 a and then the front sides of the wafers have been polished in the second polishing unit 250 b. In an alternative embodiment, it is also possible to polish the front sides of the wafers in the first polishing unit 250 a and then polish the backsides of the wafers in the second polishing unit 250 b. In this alternative embodiment, the wafers are transferred to the first load-unload stations 15 a and 15 a′ by the second wafer transport device 160 such that the front sides of the wafers face the first load-unload station 15 a and 15 b, and transferred from the second load-unload stations 15 b and 15 b′ to the third load-unload stations 15 c and 15 c′ by the wafer turn-over device 50 such that the backsides of the wafers face the third load-unload stations 15 c and 15 c′.

With reference to FIGS. 1 and 2, an alternative method of processing semiconductor wafers in the polishing apparatus 10 according to an alternative embodiment of the present invention is described.

First, the first wafer transport device 150 transfers semiconductor wafers from the storage station 102 to the input buffer station 105.

Next, the second wafer transport device 160 transfers the wafers from the input buffer station 105 to the first two load-unload stations 15 a and 15 a′ such that first sides (front or back sides) of the wafers face the first load-unload stations 15 a and 15 a′.

Next, the wafer carriers 262 a and 262 a′ of the first polishing unit 250 a (1) move linearly to the first two load-unload stations 15 a and 15 a′, respectively, from their initial positions over the polishing table 256 a, (2) receive the wafers from the first load-unload stations 15 a and 15 a′, and then (3) return to the polishing table 256 a of the first polishing unit 250 a.

Next, the wafer carriers 262 a and 262 a′ move down to the polishing pad 255 a of the polishing table 256 a and then polish the wafers using a first slurry. Thus, the first sides of the wafers are polished on the polishing pad 255 a.

Next, after the wafers are polished on the polishing pad 255 a, the wafer carriers 262 a and 262 a′ move up from the polishing pad 255 a.

Next, the wafer carriers 262 a and 262 a′ of the first polishing unit 250 a (1) move linearly to the third two load-unload stations 15 c and 15 c′, respectively, (2) transfer the wafers to the third load-unload stations 15 c and 15 c′ such that the first sides of the wafers face the third load-unload stations 15 c and 15 c′, and then (3) return to the first load-unload stations 15 a and 15 a′.

Next, the wafer carriers 262 b and 262 b′ of the second polishing unit 250 b (1) move linearly to the third load-unload stations 15 c and 15 c′, respectively, from their initial positions over the polishing table 256 b, (2) receive the wafers from the third load-unload stations 15 c and 15 c′, and then (3) return to the polishing table 256 b of the second polishing unit 250 b.

Next, the wafer carriers 262 b and 262 b′ move down to the polishing pad 255 b of the polishing table 256 b and then polish the wafers using a second slurry, whose components are different from the first slurry. Alternatively, the first slurry used at the polishing table 256 a can be used at the polishing table 256 b instead of the second slurry. Thus, the first sides of the wafers are again polished on the polishing pad 255 b.

Next, after the wafers are polished on the polishing pad 255 b, the wafer carriers 262 b and 262 b′ move up from the polishing pad 255 b.

Next, the wafer carriers 262 b and 262 b′ of the second polishing unit 250 b (1) move linearly to the fourth load-unload stations 15 d and 15 d′, respectively, (2) transfer the wafers to the fourth load-unload stations 15 d and 15 d′ such that the first sides of the wafers face the fourth load-unload stations 15 d and 15 d′, and then (3) return to the third load-unload stations 15 c and 15 c′.

Next, the third wafer transport device 210 removes the wafers from the fourth load-unload stations 15 d and 15 d′ and then transfers the wafers to the wafer receiving stations 222 of the wafer cleaners 220 and 220′. The third wafer transport device 210 may turn over the wafers before transferring the wafers to the wafer receiving stations 222.

Next, the first wafer transport device 150 removes the wafers from the output buffer stations 230 of the wafer cleaners 220 and 220′ after the wafers have been processed in the wafer cleaners 220 and 220′.

Next, the first wafer transport device 150 transfers the wafers to the storage station 102.

With reference to FIGS. 1 and 2, another alternative method of processing semiconductor wafers in the polishing apparatus 10 according to another alternative embodiment of the present invention is described.

First, the first wafer transport device 150 transfers wafers from the storage station 102 to the input buffer station 105.

Next, the second wafer transport device 160 transfers the wafers from the input buffer station 105 to the first two load-unload stations 15 a and 15 a′ such that first sides (front or back sides) of the wafers face the first load-unload stations 15 a and 15 a′.

Next, the wafer carriers 262 a and 262 a′ of the first polishing unit 250 a (1) move linearly to the first two load-unload stations 15 a and 15 a′, respectively, from their initial positions over the polishing table 256 a, (2) receive the wafers from the first load-unload stations 15 a and 15 a′, and then (3) return to the polishing table 256 a of the first polishing unit 250 a.

Next, the wafer carriers 262 a and 262 a′ move down to the polishing pad 255 a of the polishing table 256 a and then polish the wafers using a first slurry. Thus, the first sides of the wafers are polished on the polishing pad 255 a.

Next, after the wafers are polished on the polishing pad 255 a, the wafer carriers 262 a and 262 a′ move up from the polishing pad 255 a.

Next, the wafer carriers 262 a and 262 a′ of the first polishing unit 250 a (1) move linearly to the second two load-unload stations 15 b and 15 b′, respectively, (2) transfer the wafers to the second load-unload stations 15 b and 15 b′ such that the first sides of the wafers face the second load-unload stations 15 b and 15 b′, and then (3) return to the first load-unload stations 15 a and 15 a′.

Next, the wafer carriers 262 b and 262 b′ of the second polishing unit 250 b (1) move linearly to the second load-unload stations 15 b and 15 b′, respectively, from their initial positions over the polishing table 256 b, (2) receive the wafers from the second load-unload stations 15 b and 15 b′, and then (3) return to the polishing table 256 b of the second polishing unit 250 b.

Next, the wafer carriers 262 b and 262 b′ move down to the polishing pad 255 b of the polishing table 256 b and then polish the wafers using a second slurry, whose components are different from the first slurry. Alternatively, the first slurry used at the polishing table 256 a can be used at the polishing table 256 b instead of the second slurry. Thus, the first sides of the wafers are again polished on the polishing pad 255 b.

Next, after the wafers are polished on the polishing pad 255 b, the wafer carriers 262 b and 262 b′ move up from the polishing pad 255 b.

Next, the wafer carriers 262 b and 262 b′ of the second polishing unit 250 b (1) move linearly to the fourth load-unload stations 15 d and 15 d′, respectively, (2) transfer the wafers to the fourth load-unload stations 15 d and 15 d′ such that the first sides of the wafers face the fourth load-unload stations 15 d and 15 d′, and then (3) return to the second load-unload stations 15 b and 15 b′.

Next, the third wafer transport device 210 removes the wafers from the fourth load-unload stations 15 d and 15 d′ and then transfers the wafers to the wafer receiving stations 222 of the wafer cleaners 220 and 220′. The third wafer transport device 210 may turn over the wafers before transferring the wafers to the wafer receiving stations 222.

Next, the first wafer transport device 150 removes the wafers from the output buffer stations 230 of the wafer cleaners 220 and 220′ after the wafers have been processed in the wafer cleaners 220 and 220′.

Next, the first wafer transport device 150 transfer the wafers to the storage station 102.

With reference to FIG. 6, a polishing station 20A in accordance with an embodiment of the present invention is described. FIG. 6 is a top view of the polishing station 20A. The polishing station 20A is similar to the polishing station 20 of FIG. 1 except that the polishing station 20A comprises two wafer turn-over devices 50 and 50′ while the polishing station 20 comprises only one wafer turn-over device 50. The polishing station 20A can be used in the polishing apparatus 10 instead of the polishing station 20.

The first wafer turn-over device 50 of the polishing station 20A is situated between the second load-unload station 15 b and the third load-unload station 15 c. The first wafer turn-over device 50 transfers wafers from the second load-unload station 15 b to the third load-unload station 15 c. In operation, a robotic arm of the first wafer turn-over device 50 approaches the second load-unload station 15 b to pick up the wafer from the second load-unload station 15 b. The robotic arm of the first wafer turn-over device 50 turns over the wafer after the wafer is picked up from the second load-unload station 15 b such that the wafer is transferred to the third load-unload station 15 c after the wafer is turned over.

The second wafer turn-over device 50′ of the polishing station 20A is situated between the second load-unload station 15 b′ and the third load-unload station 15 c′. The second wafer turn-over device 50′ transfers wafers from the second load-unload station 15 b′ to the third load-unload station 15 c′. In operation, a robotic arm of the turn-over device 50′ approaches the second load-unload station 15 b′ to pick up the wafer from the second load-unload station 15 b′. The robotic arm of the wafer turn-over device 50′ turns over the wafer after the wafer is picked up from the second load-unload station 15 b′ such that the wafer is transferred to the third load-unload station 15 c′ after the wafer is turned over.

With reference to FIG. 6, a method of processing semiconductor wafers in the polishing apparatus 10 with the polishing station 20A according to an embodiment of the present invention is described. The method of processing wafers in the polishing apparatus 10 with the polishing station 20A is similar to the method of processing wafers in the polishing apparatus 10 with the polishing station 20 except that the wafers are turned over and transferred from the second load-unload station 15 b to the third load-unload station 15 c by the first wafer turn-over device 50, and the wafers are turned over and transferred from the second load-unload station 15 b′ to the third load-unload station 15 c′ by the second wafer turn-over device 50′ in the polishing station 20A. In contrast, the wafers are turned over and transferred from the second load-unload stations 15 b and 15 b′ to the third load-unload stations 15 c and 15 c′ by the wafer turn-over device 50 in the polishing station 20.

With reference to FIGS. 7-9, a wafer turn-over device 55 according to an embodiment of the present invention is described. FIG. 7 is a top view of the wafer turn-over device 55 when the wafer turn-over device 55 is positioned over the second load-unload station 15 b to pick up a semiconductor wafer W from the second load-unload station 15 b. In FIG. 7, the backside of the wafer W is facing downward toward the second load-unload station 15 b. FIG. 8 is a top view of the wafer turn-over device 55 when the turn-over device 55 is positioned over the third load-unload station 15 c to release the wafer onto the third load-unload station 15 c. In FIG. 8, the front side of the wafer W is facing downward toward the third load-unload station 15 c. FIG. 9 is a vertical cross-sectional view of the wafer turn-over device 55 along the line XX in FIG. 7. The wafer turn-over device 55 can replace the wafer turn-over device 50 in the polishing station 20 or can replace each of the wafer turn-over devices 50 and 50′ in the polishing station 20A.

The wafer turn-over device 55 comprises a first gripping assembly 60 a, a second gripping assembly 60 b, a support structure 65 and a pivoting mechanism 70. The support structure 65 is connected to the pivoting mechanism 70 such that the pivoting mechanism 70 pivots the support structure 65 about a pivoting axis 72, as shown in FIG. 7.

The first gripping assembly 60 a comprises a gripping arm 71 a, grippers 72, a linear moving mechanism 73 a and a stopper 74 a. The linear moving mechanism 73 a is mounted to the support structure 65. The gripping arm 71 a is operably coupled to the support structure 65 at an aperture of the gripping arm 71 a in a movable manner such that the gripping arm 71 a can be moved linearly along the support structure 65 by the linear moving mechanism 73 a, which is coupled to the gripping arm 71 a. The stopper 74 a is mounted to the support structure 65 such that the linear motion of the gripping arm 71 a along the support structure 65 is stopped when the gripping arm 71 a contacts the stopper 74 a.

The second gripping assembly 60 b comprises a gripping arm 71 b, grippers 72, a linear moving mechanism 73 b and a stopper 74 b. The linear moving mechanism 73 b is mounted to the support structure 65. The gripping arm 71 b is operably coupled to the support structure 65 at an aperture of the gripping arm 71 b in a movable manner such that the gripping arm 71 b can be moved linearly along the support structure 65 by the linear moving mechanism 73 b, which is coupled to the gripping arm 71 b. The stopper 74 b is mounted to the support structure 65 such that the linear motion of the gripping arm 71 b along the support structure 65 is stopped when the gripping arm 71 b contacts the stopper 74 b.

In order to grip the wafer on the second load-unload station 15 b, the gripping arms 71 a and 71 b are moved close to each other by their respective linear moving mechanisms 73 a and 73 b, as illustrated in FIG. 6 by the arrows M, until the gripping arms contact their respective stoppers 74 a and 74 b. In order to release the wafer onto the third load-unload station 15 c, the gripping arms 71 a and 71 b are moved away from each other by their respective linear moving mechanisms 73 a and 73 b, as illustrated in FIG. 8 by the arrows N.

Each of the grippers 72 is configured to have a “

” shape, as illustrated in FIG. 9. The grippers 72 are mounted to their respective gripping arms 71 a and 71 b such that edge region of the wafer is confined in the “

” shaped grippers when the gripping arms are in contact with their respective stoppers 74 a and 74 b. It is noted that the lifter 200 of the load-unload station 15 is lifted to the wafer transfer position, as illustrated in FIG. 4, when the wafer turn-over device 50 grips the wafer in the second load-unload station 15 b and when the wafer turn-over device 50 releases the wafer onto the third load-unload station 15 c.

Turning back to FIGS. 7 and 8, the pivoting mechanism 70 turns over the wafer confined by the grippers 72 by pivoting the support structure 65 about the axis 72. The axis 72 is vertical to the line defined by the centers 16 b and 16 c of the second and third load-unload stations 15 b and 15 c, respectively. The axis 72 is also configured to be parallel to the wafers positioned on the second and third load-unload stations 15 b and 15 c.

The pivoting mechanism 70 may be further configured to pivot the support structure 65 about an axis 75 that is parallel to the line defined by the centers 16 b and 16 c of the second and third load-unload stations 15 b and 15 c, respectively, such that the gripping assemblies 60 a and 60 b are moved away from the second and third load-unload stations 15 b and 15 c, as illustrated in FIG. 10. FIG. 10 is a top view of the second and third load-unload station 15 b and 15 c and the wafer turn-over device 55 when the gripping assemblies 60 a and 60 b are pivoted away from the second load-unload station 15 b about the axis 75.

With reference to FIG. 11, a polishing station 20B in accordance with an embodiment of the present invention is described. FIG. 11 is a top view of the polishing station 20B. The polishing station 20B is similar to the polishing stations 20 and 20A except that the polishing station 20B further comprises two washing stations 18 and 18′. Although the polishing station 20B is shown in FIG. 11 as comprising the wafer turn-over devices 50 and 50′, the polishing station 20B may comprise only the wafer turn-over device 50, similar to the polishing station 20. The polishing station 20B can be used in the polishing apparatus 10 instead of the polishing station 20.

The first washing station 18 is situated between the second polishing table 256 b and the fourth load-unload station 15 d such that the wafer carrier 262 b of the second polishing unit 250 b can be positioned over the washing station 18. The second washing station 18′ is situated between the second polishing table 256 b and the fourth load-unload station 15 d′ such that the wafer carrier 262 b′ of the second polishing unit 250 b can be positioned over the washing station 18′.

With reference to FIG. 12, the washing station 18 in accordance with an embodiment of the invention is described. FIG. 12 is a top view of the washing station 18. The washing station 18 is similar to the load-unload station 15 except that the washing station does not comprise the lifter 200, the lift piston 202, the lift cylinder 204, the wafer tray 211 and the first fluid channel 270 of the load-unload station 15. The washing station 18 is used to wash the wafer carrier 262 b of the second polishing unit 250 b when the wafer carrier 262 b is positioned over the washing station 18 after the wafer carrier 262 b transfers a wafer to the fourth load-unload station 15 d. In order to wash the wafer carrier 262 b, D.I. water is sprayed onto the wafer carrier 262 b. The washing station 18′ is similar to the washing station 18. The washing station 18′ is used to wash the wafer carrier 262 b′ of the second polishing unit 250 b when the wafer carrier 262 b′ is positioned over the washing station 18′ after the wafer carrier 262 b′ transfers a wafer to the fourth load-unload station 15 d′.

In an alternative embodiment of the polishing station 20B, the first washing station 18 is situated between the second polishing table 256 b and the third load-unload station 15 c such that the wafer carrier 262 b of the second polishing unit 250 b can be positioned over the washing station 18. The second washing station 18′ is situated between the second polishing table 256 b and the third load-unload station 15 c′ such that the wafer carrier 262 a′ of the second polishing unit 250 b can be positioned over the washing station 18′.

In another alternative embodiment of the polishing station 20B, the first washing station 18 is situated between the first polishing table 256 a and the second load-unload station 15 b such that the wafer carrier 262 a of the first polishing unit 250 a can be positioned over the washing station 18. The second washing station 18′ is situated between the first polishing table 256 a and the second load-unload station 15 b′ such that the wafer carrier 262 a′ of the first polishing unit 250 a can be positioned over the washing station 18′.

In another alternative embodiment of the polishing station 20B, the first washing station 18 is situated between the first polishing table 256 a and the first load-unload station 15 a such that the wafer carrier 262 a of the first polishing unit 250 a can be positioned over the washing station 18. The second washing station 18′ is situated between the first polishing table 256 a and the first load-unload station 15 a′ such that the wafer carrier 262 a′ of the first polishing unit 250 a can be positioned over the washing station 18′.

With reference to FIG. 11, a method of processing semiconductor wafers in the polishing apparatus 10 with the polishing station 20B according to an embodiment of the present invention is described. The method of processing wafers in the polishing apparatus 10 with the polishing station 20B is similar to the method of processing wafers in the polishing apparatus 10 with the polishing station 20 or with the polishing station 20A except that the wafer carriers 262 b and 262 b′ are washed at the washing stations 18 and 18′, respectively, after the wafers are transferred to the load-unload stations 15 d and 15 d′. In other embodiments in which the washing stations 18 and 18′ are located at other locations, the wafer carriers 262 a and 262 a′ or 262 b and 262 b′ are washed at the washing stations 18 and 18′, respectively, after the wafers are transferred to the load-unload stations 15 b and 15 b′ by the wafer carriers 262 a and 262 a′ or after the wafer are transferred to the load-unload stations 15 d and 15 d′ by the wafer carriers 262 b and 262 b′.

With reference to a process flow diagram of FIG. 13, a method for polishing semiconductor wafers in accordance with an embodiment of the invention is described. At block 1302, a semiconductor wafer is moved between a first load-unload station, a first polishing table and a second load-unload station on a first wafer carrier assembly. In addition, at block 1302, a first side of the semiconductor wafer is polished on the first polishing table using the first wafer carrier assembly. At block 1304, the semiconductor wafer is moved between a third load-unload station, a second polishing table and a fourth load-unload station on a second wafer carrier assembly. In addition, at block 1304, a second side of the semiconductor wafer is polished on the second polishing table using the second wafer carrier assembly. At block 1306, the semiconductor wafer is transferred from the second load-unload station to the third load-unload station using a turn-over robotic wafer handing device. In addition, at block 1306, the semiconductor wafer is turned over when the semiconductor wafer is transferred from the second load-unload station to the third load-unload station.

Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents. 

1. A polishing apparatus comprising: first and second polishing units, each of the first and second polishing units being configured to polish one side of semiconductor wafers, each of the first and second polishing units comprising: a polishing table; and a wafer carrier assembly configured to hold a semiconductor wafer and move the semiconductor wafer to and from the polishing table, the wafer carrier assembly being further configured to move the semiconductor wafer onto the polishing table; first, second, third and fourth load-unload stations, each of the first, second, third and fourth load-unload stations being configured to accommodate one of the semiconductor wafers at a time, the first and second load-unload stations being situated such that the first polishing unit is positioned between the first and second load-unload stations, the third and fourth load-unload stations being situated such that the second polishing unit is positioned between the third and fourth load-unload stations; and a turn-over robotic wafer handing device positioned between the second and third load-unload stations, the turn-over robotic wafer handing device being configured to transfer the semiconductor wafer from the second load-unload station to the third load-unload station, the turn-over robotic wafer handing device being further configured to turn over the semiconductor wafer when the semiconductor wafer is transferred from the second load-unload station to the third load-unload station.
 2. The apparatus of claim 1 wherein the first, second, third and fourth load-unload stations are all arranged in a linear manner.
 3. The apparatus of claim 1 wherein at least one of the first, second, third and fourth load-unload stations is configured to spray fluid onto a wafer carrier of the wafer carrier assembly or the semiconductor wafer when the wafer carrier or the semiconductor wafer is positioned at that load-unload station.
 4. The apparatus of claim 1 further comprising a washing station positioned between the first and fourth load-unload stations, the washing station being configured to spray fluid onto a wafer carrier of the wafer carrier assembly when the wafer carrier is positioned over the washing station.
 5. The apparatus of claim 4 wherein the washing station is positioned between the first load-unload station and the polishing table of the first polishing unit, between the polishing table of the first polishing unit and the second load-unload station, between the third load-unload station and the polishing table of the second polishing unit, or between the polishing table of the second polishing unit and the fourth load-unload station.
 6. The apparatus of claim 1 wherein the wafer carrier assembly of the first polishing unit is configured to be moved between the first load-unload station, the polishing table of the first polishing unit and the second load-unload station, and wherein the wafer carrier assembly of the second polishing unit is configured to be moved between the third load-unload station, the polishing table of the second polishing unit and the fourth load-unload station.
 7. The apparatus of claim 1 wherein the wafer carrier assembly of the first polishing unit is configured to be moved between the first load-unload station, the polishing table of the first polishing unit and the third load-unload station, and wherein the wafer carrier assembly of the second polishing unit is configured to be moved between the third load-unload station, the polishing table of the second polishing unit and the fourth load-unload station.
 8. The apparatus of claim 1 wherein the wafer carrier assembly of the first polishing unit is configured to be moved between the first load-unload station, the polishing table of the first polishing unit and the second load-unload station, and wherein the wafer carrier assembly of the second polishing unit is configured to be moved between the second load-unload station, the polishing table of the second polishing unit and the fourth load-unload station.
 9. The apparatus of claim 1 further comprising: another first, second, third and fourth load-unload stations, the another first and second load-unload stations being situated such that the first polishing unit is positioned between the another first and second load-unload stations, the another third and fourth load-unload stations being situated such that the second polishing unit is positioned between the another third and fourth load-unload stations, wherein each of the first and second polishing units further comprises another wafer carrier assembly configured to hold another semiconductor wafer and move the another semiconductor wafer to and from the polishing table, the wafer carrier assembly being further configured to polish the another semiconductor wafer on the polishing table.
 10. The apparatus of claim 9 wherein the another first, second, third and fourth load-unload stations are all arranged in a linear manner.
 11. The apparatus of claim 9 wherein the turn-over robotic wafer handing device is further configured to transfer the another semiconductor wafer from the another second load-unload station to the another third load-unload station.
 12. The apparatus of claim 9 further comprising another turn-over robotic wafer handing device positioned between the another second load-unload station and the another third load-unload station, the another turn-over robotic wafer handing device being configured to transfer the another semiconductor wafer from the another second load-unload station to the another third load-unload station.
 13. A method for polishing semiconductor wafers, the method comprising: moving a semiconductor wafer between a first load-unload station, a first polishing table and a second load-unload station on a first wafer carrier assembly, including polishing a first side of the semiconductor wafer on the first polishing table using the first wafer carrier assembly; moving the semiconductor wafer between a third load-unload station, a second polishing table and a fourth load-unload station on a second wafer carrier assembly, including polishing a second side of the semiconductor wafer on the second polishing table using the second wafer carrier assembly; and transferring the semiconductor wafer from the second load-unload station to the third load-unload station using a turn-over robotic wafer handing device, including turning over the semiconductor wafer when the semiconductor wafer is transferred from the second load-unload station to the third load-unload station.
 14. The method of claim 13 wherein the moving the semiconductor wafer between the first load-unload station, the first polishing table and the second load-unload station includes linearly moving the first wafer carrier assembly between the first load-unload station, the first polishing table and the second load-unload station of the first polishing unit.
 15. The method of claim 13 further comprising: moving another semiconductor wafer between another first load-unload station, the first polishing table and another second load-unload station on another first wafer carrier assembly, including polishing a first side of the another semiconductor wafer on the first polishing pad using the another first wafer carrier assembly; and moving the another semiconductor wafer between another third load-unload station, the second polishing table and another fourth load-unload station on another second wafer carrier assembly, including polishing a second side of the another semiconductor wafer on the second polishing table using the another second wafer carrier assembly.
 16. The method of claim 15 wherein the moving the another semiconductor wafer between the another first load-unload station, the first polishing table and the another second load-unload station includes linearly moving the another first wafer carrier assembly between the another first load-unload station, the first polishing table and the another second load-unload station.
 17. The method of claim 15 further comprising transferring the another semiconductor wafer from the another second load-unload station to the another third load-unload station using the turn-over robotic wafer handing device.
 18. The method of claim 15 further comprising transferring the another semiconductor wafer from the another second load-unload station to the another third load-unload station using another turn-over robotic wafer handing device.
 19. The method of claim 13 further comprising: transferring the semiconductor wafer from a wafer storage station to a buffer station; transferring the semiconductor wafer from the buffer station to the first load-unload station; transferring the semiconductor wafer from the fourth load-unload station to a wafer cleaner; and transferring the semiconductor wafer from the wafer cleaner to the wafer storage station. 